1. Field of the Invention
The present invention relates to a microwave oven, and more particularly, an improved microwave oven having a cooking chamber, a fan housing attached to the cooking chamber, and a convection heater mounted on an air passageway formed between the cooking chamber and the fan housing.
2. Description of the Related Art
A microwave oven having a convection heater has been used for efficiently cooking food placed in a cooking chamber while the food is cooked by microwaves. Typically, the convection heater is mounted on a sidewall of a fan housing attached to the cooking chamber. For example, a conventional microwave oven shown in FIGS. 1 and 2 includes a main body 101 and a cooking chamber 103 formed in the main body 101. In the front of the main body 101 are provided a door 105 opening and closing the cooking chamber 103 and a control panel 107 operating the microwave oven. In the rear of the control panel 107 is formed a component chamber in which a number of components operating cooking functions of the microwave oven are installed.
On the bottom of the cooking chamber 103, a circular tray 109 on which the food is put is rotatably installed. The circular tray 109 is rotated by a driving motor not shown. A fan housing 130 is formed at the rear of the cooking chamber 103 and between a partition 110 and a heater casing 131. In the fan housing 130 are installed a convection heater 121 generating heat by means of an external power supply and a ventilator sending air heated by the convection heater 121 into the cooking chamber 103.
On the partition 110 are formed a number of air suction holes 111 and air discharge holes 123 circulating air heated by the convection heater 121 between the cooking chamber 103 and the fan housing 131. The air suction holes 111 are formed in the central area of the partition 110 and are in communication with the fan housing 130. The air discharge holes 123 are formed along the circumferential area of the partition 110 and are in communication with the fan housing 130. The convection heater 121 having a form of loop mounted adjacent to the air discharge holes 123 on the partition 110 and is fixed on the back face of the partition 110 by a plurality of brackets 135. The fan 133 mounted on heater casing 131 is disposed in the rear area of the convection heater 121 and adjacent to the air suction holes 111 formed on the partition 110 to suck the air from cooking chamber 103 into the inside of the fan housing 130 through the air suction holes 111 and blow the air sucked into the fan housing 130 toward the air discharge holes 123.
With this configuration, when the microwave oven operates, the convection heater 121 heats the air within the fan housing 130. Then, the fan 133 blows the heated air in the radial direction. The heated air in the fan housing 130 is discharged into the cooking chamber 103 through the air discharge holes 123, and thereby cooking the food in the cooking chamber 103. The air blown into the cooking chamber 103 returns to the fan housing 130 through the air suction holes 111 by the suction force of the fan 133. The returning air is heated by the convection heater 121 and transferred into the cooking chamber 103 by the fan 133, thereby forming air circulation.
However, since the convection heater is installed in the fan housing isolated from the cooking chamber and is not located on an air passageway, the heat energy of the convection heater is consumed to increase temperature of the inner side of the fan housing and the remaining heat energy is consumed to heat the air blown into the cooking chamber through the air discharge holes. Thus, there occurs a loss of heat by the amount of the heat which is used to heat the fan housing, thereby lowering efficiency of cooking in the microwave oven. Furthermore, to prevent heat from being transferred into a driving motor of the fan and an electric wire, etc., and being emitted outside of the cooking chamber and the fan housing, an insulating member is required around the convection heater, thereby increasing the cost of production.